feat: prefetch assets

[Neonkraft]

Summary

Adds a prefetch_assets: bool = True field to PostTrainingConfig (src/post_training/config.py) and updates scripts/submit.py so the login-node prefetch step (HF cache env application + prefetch_assets(config)) runs whenever config.offline or config.prefetch_assets is true. Previously prefetching only ran under offline: true; it's now on by default independent of offline mode, with an opt-out via prefetch_assets: false.

Type of change

• Bug fix
• New feature
• Refactor
• Performance
• Documentation
• Maintenance

Validation

Describe how this change was verified.

[Copilot]

Pull request overview

This PR introduces a new top-level configuration flag to control whether models/datasets are pre-fetched on the login node before SLURM submission, and updates the submission script + documentation so prefetching can run independently of offline mode (enabled by default, with opt-out).

Changes:

• Add prefetch_assets: bool = True to PostTrainingConfig.
• Update scripts/submit.py so the prefetch step runs when offline or prefetch_assets is true.
• Document the new prefetch_assets flag and add it to the example config in README.md.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/post_training/config.py	Adds prefetch_assets flag (default True) to the root config schema.
scripts/submit.py	Runs login-node prefetch when offline or prefetch_assets is enabled.
README.md	Documents prefetch behavior and adds prefetch_assets to the sample config.

Comments suppressed due to low confidence (1)

scripts/submit.py:122

• The prefetch log message is now misleading: this block runs when either offline or prefetch_assets is true, but it always logs offline=True. This will confuse users who have offline: false and are only using prefetching.

        logger.info(
            "offline=True: pre-fetching models and datasets on the login node "
            "before submitting the job."
        )

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